Debugging Sensitivity to C math library on Linux

C math library functions, such as exp or sin, are not guaranteed to be “precise”. The results might be slightly different on different platforms. A recent change in mingw-w64 v12, which is a core dependency of compilers we use on Windows (both GCC and LLVM), resulted in failures in about 20 CRAN packages. Rtools45 uses mingw-w64 v11, the same version as Rtools44, to allow time for resolving the issues. The change in mingw-w64 v12 switched about 90 math functions from internal implementations to UCRT, the Windows C runtime provided by Microsoft and shipped with the OS.